6.65
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
of-section faults behind the local terminal. Zone 3 phase-distance element reach
was set to coordinate with the largest remote Zone 2 phase-distance element
reach.
Z3MG = Z3MP = 50.50
Z3MG := 50.50. Zone 3 (OFF, 0.05–64 secondary)
Zero-Sequence Current Compensation Factors
Zero-sequence current compensation helps to keep the phase and ground-dis-
tance elements at the same reach if you set the reach equal per zone (for example,
Z1MP = Z1MG). Ground-distance elements should measure fault impedance in
terms of positive-sequence impedance only. The relay automatically calculates
the setting for the Zone 1 zero-sequence current compensation factor when you
set k0M1 to AUTO.
k0M1 := AUTO. Zone 1 ZSC Factor Magnitude (AUTO, 0.000–10)
When you enter AUTO as the setting for k0M1, the relay calculates the zero-
sequence current compensation as follows:
Equation 6.32
Zone 2 and Zone 3 use the same zero-sequence current compensation factor as
that for Zone 1 because Advanced Settings are disabled.
The relay displays the following values for k0M1 and k0MA:
k0M1 := 0.750. Zone 1 ZSC Factor Magnitude (AUTO, 0.000–10)
k0MA := -16.87. Zone 1 ZCS Factor Angle (–180.0 to +180.0 degrees)
Distance Element Common Time Delay
NOTE: If the relay is using a remote
data acquisition system, such as TiDL,
the operating times will be delayed by
1.5 ms. Use caution when setting the
relay coordination times to account
for this added delay.
Set the appropriate timers Z1D, Z2D, and Z3D for both phase and ground-dis-
tance elements.
You do not need to delay Zone 1 distance protection; it trips instantaneously.
Z1D := 0.000. Zone 1 Time Delay (OFF, 0.000–16000 cycles)
Zone 2 distance protection provides time-delayed tripping as a backup function.
Set this delay to 20 cycles.
Z2D := 20.000. Zone 2 Time Delay (OFF, 0.000–16000 cycles)
Zone 3 distance protection is reverse-looking and you do not need to apply it for
tripping in this application. Set Zone 3 for zero time delay.
Z3D := 0.000. Zone 3 Time Delay (OFF, 0.000–16000 cycles)
SOTF Scheme
SOTF logic is enabled when the circuit breaker closes. This logic provides pro-
tection for a short duration (setting SOTFD) until other protection (such as trip-
ping from SEL
OGIC control equations TR, TRCOMM, and TRCOMMD) is
available. The TRSOTF SEL
OGIC control equation defines which protection ele-
k01
Z0MAG Z0ANG Z1MAG Z1ANG–
3 Z1MAG Z1ANG•
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